With the development of Internet, a distributed system cannot better satisfy the requirement of the network scalability and management, and therefore, a control and forwarding separation centralized system emerges as the times require. For example: an open flow (OpenFlow) system is a kind of control and forwarding separation centralized system, and an OpenFlow switch (OpenFlow Switch) transforms a packet forwarding process controlled originally and entirely by a switch/router into a process completed by the OpenFlow switch and a controller (Controller) collectively, thereby implementing the separation of data forwarding and routing control. The controller may control a flow table of the OpenFlow switch through an interface operation stipulated in advance, thereby achieving the objective of controlling data forwarding. For a packet entering the OpenFlow switch, the OpenFlow switch may obtain a flow table entry matched with the packet by querying the flow table. According to the flow table entry, an operation required to be executed on the packet may be determined, and the operation, for example, may be to forward the packet to a destination port, to discard the packet or to report the packet to the controller. For the first packet of a flow, the OpenFlow switch may report the packet to the controller because no flow table entry is obtained by matching, and the controller establishes a new flow table entry for the flow to which the packet belongs, and delivers the packet to the OpenFlow switch, so that the OpenFlow switch adds the new flow table entry to the flow table.
However, when all flow table entry resources are in use, the OpenFlow switch cannot add the new flow table entry to the flow table, so that the OpenFlow switch cannot perform timely processing on the new flow, so as to cause the reduction of the reliability of packet processing. Similar problems also exist in other control and forwarding separation centralized systems.